Solve for $q$ : $29 = q + 21$
Subtract $21$ from both sides: $ \begin{eqnarray} \\ \hphantom{29 {- 21}} &\hphantom{=}& \hphantom{q} \\ 29 &=& q + 21 \\ \\ {-21} && {-21} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ 29 {- 21} &=& q \\ \end{eqnarray} $ Simplify. $ q = 8$